The present invention relates in general to panels or housings for solar energy cells. More particularly, it relates to panels in which the solar energy cells are mounted for exposure to light while being protected from deleterious environmental conditions.
Solar energy cells are semiconductor devices used to convert light into electricity. Generally, once solar energy cells are exposed to light, they develop a voltage across their terminals and a consequent flow of electrons, such flow being related to the intensity of the light impinging on the photovoltaic junction formed at the surface of the cell. Where a plurality of cells are utilized, they are interconnected in such size and number to produce the desired voltage required for operation of the load or for battery storage. During their exposure to light, which is ordinarily sunlight, the cells and the panels in which they are housed often experience an increase in temperature, such rise in temperature being due to the heat generated by the light impinging on the cell. Under normal operation, solar cells have a lower efficiency at higher temperatures. Consequently, a decrease in efficiency is often effected by the increased temperatures. Thereby, despite the strong light concentration, the output is lower than expected upon direct exposure of cells to high light levels.
While a slight decrease in efficiency of operation of solar energy cells exposed to high light intensities may be tolerable in some instances, it is nevertheless desirable to cool the cells by some means. This is especially true if the solar cells are to be exposed to light intensities greater than one sun. This is the case when light concentrators are utilized. Such concentrators may be lenses, mirrors, or other means used to focus light from the sun. When the light rays are concentrated and are directed or reflected on the cells, an increased flow of electrons results.
The use of concentrators to focus the light on solar energy cells results in a magnification of the problem that might, under circumstances where no concentrators are utilized, be tolerable. Thus, if a concentrator is capable of increasing the light intensity from the sun on a solar energy cell by a multiple of three, then the electricity that the cell generates from such light will be substantially increased, optimally by the same factor of three. Under such conditions, however, the temperature of the cell will rise considerably and there will be a corresponding decrease in cell efficiency. As a result, particularly when concentrators are used but also when optimum efficiency is necessary for solar cells exposed only to ambient light, it is highly desirable to cool the cells, and thereby maintain maximum cell efficiency.
It is, therefore, a primary object of the present invention to produce a solar energy cell panel that will enable heat generated by impingement of light on the cells to be rapidly dissipated from the immediate environment of the cells while concomitantly failing to conduct electricity generated by the cell junctions away from the cells. In this manner, the loss of electricity generated is made minimal while the transfer of heat away from the cells--and consequent loss of efficiency by the cells--is maximized.
It is another object of the present invention to provide a panel for mounting solar energy cells in which the cells will be protected from environmental conditions.
It is still another object of the present invention to provide for a dual generation of energy from the sun's rays: the generation of electricity by photovoltaic cells and the simultaneous generation and conduction of heat away from the immediate environment of the cells to a location at which such heat can be utilized.
The present invention is a panel on which solar energy cells are mounted for exposure to light. Basically, it comprises an enclosure or housing for holding the cells, which enclosure or housing has at least one wall formed from a good conductor of heat. Generally the entire enclosure will be formed from a heat conductive metal, although such is not necessarily requisite. Within the enclosure is a somewhat resilient, resinous cushion that is a relatively good conductor of heat and a relatively poor conductor of electricity. That cushion occupies a substantial portion of the interior of the enclosure and has at least one surface in heat transfer position with respect to the enclosure wall that is formed of the good conductor of heat. Another surface of the cushion is substantially unobstructed to the impingement of light thereon.
Solar energy cells, which ordinarily are utilized in multiples of cells but may be a single cell, are secured to the cushion at the surface thereof that is exposed to light. In this way, light that impinges on the cells will generate a flow of electricity that is directed away from the cells and either stored or used to operate equipment, and heat generated by the light impinging on the cells and on the panel itself will be conducted by the cushion to the wall of the enclosure that is a good conductor of heat and, if desired, away from that wall by other means. Such further means may desirably include a conduit, one of the walls of which is formed by the other side of said heat-conductive enclosure wall. With inlet and outlet ducts, the conduit can be utilized to pass fluids, e.g. air or water, into and out of contact with the other side of the heat-conductive enclosure wall, and heat will thereby be removed from the wall. Particularly, for example, when the fluid is water or some other conductor of heat, the heat so generated may be stored or put to other use, so that by this particular construction both heat and electricity generated by impingement of light on solar energy cells and their mounting structure will be put to desired uses.
In order to protect the cells from the environment, the light-impinging surfaces of the cells are protected by a material that will be transparent to the passage of light, yet will furnish a shield against wind, rain, dust particles and the like. Consequently, in one embodiment of the invention, silicone rubber has been used to form a protective sheet over the cells. In order to ensure stability of the cells so far as motion is concerned, they are generally adhered at their exposed junction surface to the silicone rubber protective sheet, and at their opposite surface to the resinous cushion on which they are mounted. In such position the cells will be substantially protected from ambient conditions, yet be capable of functioning at a high efficiency even when light greater than one sun is directed on their photovoltaic junctions.